In fact, in a recent episode of the mindbodygreen podcast, Bredesen explains that dangerously low levels of vitamin D [i.e., 25(OH)D serum test results at or below 20 ng/ml—the clinical cutoff for vitamin D deficiency] is one of the main contributing factors of cognitive decline he sees in his patients.
“It is surprisingly common to see people come in with cognitive decline and their vitamin D level is 19 or 20 [ng/ml],” he shares.
How did these individuals become vitamin D deficient in the first place? According to Bredesen, it’s a combination of lifestyle habits and nutritional choices: “They’re living indoors, they’re not getting out enough, they’re not taking vitamin D, or they’re not absorbing the vitamin D they are taking.”
While getting outdoors and spending some time in the sun—safely, of course—is always recommended, the sun isn’t a historically reliable source of vitamin D. (And for the record, diet isn’t either!)
So, we’re left with supplementation. But as Bredesen stated, some people are taking vitamin D supplements and seeing no improvement to their D levels—or their cognitive function.